string_func if {
    concat("--", ["a", "b"]) == "a--b"
    split("a--b", "--") == ["a", "b"]
    contains("abcdefg", "bc") == true
    startswith("abcdefg", "abc") == true
    endswith("abcdefg", "efg") == true
    upper("abcdefg") == "ABCDEFG"
    lower("ABCDEFG") == "abcdefg"
}

format_string if {
    sprintf("%v", [10]) == "10"
    sprintf("%v-%v-%v", [10, 20, 30]) == "10-20-30"
    sprintf("%[1]v-%[2]v-%[3]v", [10, 20, 30]) == "10-20-30"
    sprintf("%[3]v-%[3]v-%[1]v", [10, 20, 30]) == "30-30-10"
}
